Not even the hottest day at the hottest place on Earth comes close to how hot it gets on Mercury. Mercury is one of the nine planets in our solar system. Mercury is the closest planet to the Sun.

HOW HOT DOES IT GET ON MERCURY?

Daytime temperatures on Mercury can soar to 810° Fahrenheit (430° Celsius). That is hot enough to melt some metals! Mercury gets so hot because it is so close to the Sun. Mercury is 36 million miles (58 million kilometers) from the Sun, on average. Its distance from the Sun changes somewhat throughout the year. Earth is about three times farther from the Sun.

It really cools off at night on Mercury. The temperature can drop as low as -290° Fahrenheit (-180° Celsius) after the Sun goes down. So Mercury doesn’t just get hotter than anywhere on Earth. It also gets colder! It gets so cold partly because Mercury has almost no atmosphere. An atmosphere is the gases around a planet. On Earth, the gases act like a blanket that holds in heat. Another reason it gets so cold is that Mercury turns slowly. On Mercury, night lasts much longer than it does on Earth, and all the heat leaks away into space.

TIME ON MERCURY

A day on Mercury is a long time. One Mercury day lasts almost 59 days on Earth. One day is the time it takes for a planet to spin once around its axis. An axis is an imaginary line going through the center of a planet. Mercury turns very slowly on its axis.

A year on Mercury, however, is pretty short. Mercury moves fast around the Sun. It takes Earth 365 days to go around the Sun, so a year on Earth is 365 days long. A year on Mercury is only 88 Earth days. That’s the time it takes Mercury to go around the Sun. Since Mercury’s year is so short and its day is so long, the planet only has 3 days for every 2 years!

WHAT IS MERCURY MADE OF?

Mercury has a surface made of rocks. Some places on Mercury are smooth. Some places have wrinkly ridges.

There are many big, round holes called craters on the surface of Mercury. Meteors and comets crash into Mercury and make the craters. Meteors are chunks of stone and metal that fall from space. Comets are balls of ice and rock. There is ice at the bottom of some deep craters near Mercury’s north and south poles. Scientists think the ice may have come from comets. Mercury has no liquid water.

Scientists think that there must be a lot of iron metal inside Mercury. They think this because Mercury is a giant magnet. Earth is also a giant magnet. Earth is a magnet because it has hot, liquid iron in its core. The liquid iron spins and makes Earth a magnet. Scientists think the same thing happens on Mercury. But Mercury is a weaker magnet than Earth.

HOW DO WE LEARN ABOUT MERCURY?

Scientists do not know as much about Mercury as they do about most of the other planets. It is hard to study Mercury, because Mercury is hard to see.

Mercury is the second smallest planet, after Pluto. Its diameter (the width of the planet) is 3,032 miles (4,879 kilometers). That is about the distance across the United States. Mercury also orbits close to the Sun. The Sun is so bright that its glare makes Mercury hard to see from Earth. Special telescopes are needed to study Mercury.

Only one spacecraft has visited Mercury. Mariner 10 flew past Mercury in 1974 and 1975. Mariner 10 took lots of pictures. It measured Mercury’s temperature. Most of what scientists know about Mercury came from Mariner 10.